Gas turbines, as well as other rotary engines, typically exhibit a rotatable rotor in a fixed housing or else a rotatable shaft. In the case of a gas turbine, the fixed components are referred to as the stator. Between the shaft (rotor) and the stator is typically arranged a flow channel for a working medium running in an axial direction. In particular, rotors in a gas turbine are customarily exposed to high mechanical and thermal loads on account of the operating conditions. The high temperatures of the working medium and the forces acting on the rotor when the gas turbine is operating mean that the rotor components are under a great deal of stress.
During assembly of the shaft and components of a rotary engine, the individual components are typically tensioned by means of a tie bar. Under normal circumstances, the tie bar is received by the shaft and arranged therein. For assembly of the shaft and components, each component typically exhibits an axially extending recess through which the tie bar runs. In order to tension the tie bar, a screw nut can be placed onto one end of the tie bar, which fixes the individual components during tensioning and applies mechanical stress to the tie bar. This means that the components are in pressing contact with one another on the tie bar and are therefore able to suitably transmit the rotatory forces acting on them when the rotary engine is in operation.
In many types of gas turbine and also in many rotary engines, clamping nuts are used with multiple clamping screws to tension the tie bar. Multiple clamping screws should be understood to be a set of individual clamping screws which, following individual tensioning, can expose the clamping nut to a sufficient total tensioning force. Due to the high temperatures that sometimes occur and can act on the clamping nut when the rotary engine is in operation, lubricant may escape at the clamping screws and microscopic deformations may also possibly occur, so that during maintenance work, for example, and the loosening of the clamping screws, one or more of these may become stuck so that they can no longer be mechanically loosened. In a case of this kind which is particularly inconvenient for the rotary engine operator, it is sometimes no longer possible for the machine to be dismantled and maintenance work carried out. In order to be able to carry out the dismantling, however, the only option available to the operator is to destroy the clamping nut in question, although this may result in the destruction of the tie bar and the entire rotary engine with it.
Furthermore, it has proved disadvantageous that during the tensioning of the tie bar the clamping force has to be applied to the clamping nut via the individual clamping screws. Since, on the one hand, the clamping nut must exhibit many individual clamping screws of this kind in order to be able to apply the high total clamping force, the tensioning process has proved very time-consuming. Furthermore, it is not impossible for some of the individual clamping screws to become twisted themselves, as from time to time some individual clamping screws contribute more to the total clamping force, comparatively speaking, than others. In other words, it is essential for all individual clamping screws to be tightened uniformly, so that during the very time-consuming tensioning process, individual clamping screws do not suffer any twisting due to the high clamping forces. Practical considerations make this very difficult, however, as even small differences in the stroke of the individual clamping screws can lead to greatly differing clamping force loads.
These disadvantages from the state of the art illustrate that a technical solution is required so that, particularly in the case of clamping nuts with multiple clamping screws, a controlled tensioning of the tie bar system and also a controlled dismantling of the entire rotary engine is furthermore possible. This means that dismantling should still be possible, even if one or more of the clamping screws gets stuck. Furthermore, it is a technical requirement for a clamping nut to be proposed which can allow easier dismantling of a rotary engine. In particular, this should apply to rotary engines which are exposed to high temperatures sometimes in excess of 350° C. in the region of the shaft (or the rotor).